/* 
 * tsh - A tiny shell program with job control
 * 
 * <Put your name and login ID here>
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE    1024   /* max line size */
#define MAXARGS     128   /* max args on a command line */
#define MAXJOBS      16   /* max jobs at any point in time */
#define MAXJID    1<<16   /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /* running in foreground */
#define BG 2    /* running in background */
#define ST 3    /* stopped */

/* 
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 * At most 1 job can be in the FG state.
 */

/* Global variables */
extern char **environ;      /* defined in libc */
char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
int verbose = 0;            /* if true, print additional output */
int nextjid = 1;            /* next job ID to allocate */
char sbuf[MAXLINE];         /* for composing sprintf messages */

struct job_t {              /* The job struct */
    pid_t pid;              /* job PID */
    int jid;                /* job ID [1, 2, ...] */
    int state;              /* UNDEF, BG, FG, or ST */
    char cmdline[MAXLINE];  /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */


/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv); 
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs); 
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid); 
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid); 
int pid2jid(pid_t pid); 
void listjobs(struct job_t *jobs);

void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine 
 */
int main(int argc, char **argv) 
{
    char c;
    char cmdline[MAXLINE];
    int emit_prompt = 1; /* emit prompt (default) */

    /* Redirect stderr to stdout (so that driver will get all output
     * on the pipe connected to stdout) */
    dup2(1, 2);

    /* Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != EOF) {
        switch (c) {
        case 'h':             /* print help message */
            usage();
	    break;
        case 'v':             /* emit additional diagnostic info */
            verbose = 1;
	    break;
        case 'p':             /* don't print a prompt */
            emit_prompt = 0;  /* handy for automatic testing */
	    break;
	default:
            usage();
	}
    }

    /* Install the signal handlers */

    /* These are the ones you will need to implement */
    Signal(SIGINT,  sigint_handler);   /* ctrl-c */
    Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
    Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */

    /* This one provides a clean way to kill the shell */
    Signal(SIGQUIT, sigquit_handler); 

    /* Initialize the job list */
    initjobs(jobs);

    /* Execute the shell's read/eval loop */
    while (1) {

	/* Read command line */
	if (emit_prompt) {
	    printf("%s", prompt);
	    fflush(stdout);
	}
	if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
	    app_error("fgets error");
	if (feof(stdin)) { /* End of file (ctrl-d) */
	    fflush(stdout);
	    exit(0);
	}

	/* Evaluate the command line */
	eval(cmdline);
	fflush(stdout);
	fflush(stdout);
    } 

    exit(0); /* control never reaches here */
}
  
/* 
 * eval - Evaluate the command line that the user has just typed in
 * 
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.  
*/
void eval(char *cmdline) 
{
    char* argv[MAXARGS];  
    int state = UNDEF;  //工作状态，FG(前台)或BG(后台) 
    static sigset_t set;
    pid_t pid;  //进程id
    static int set_ready = 0;
    if (!set_ready) {
        //把信号集 set 清零，变成“空集合”
        if (sigemptyset(&set) < 0) unix_error("sigemptyset");
        //把 SIGINT、SIGTSTP和SIGCHLD信号加入集合
        if (sigaddset(&set, SIGINT) < 0 ||
            sigaddset(&set, SIGTSTP) < 0 ||
            sigaddset(&set, SIGCHLD) < 0) unix_error("sigaddset");
        set_ready = 1;
    }
    // 处理输入的数据
    if(parseline(cmdline, argv) == 1)  //解析命令行，返回给argv数组
        state = BG;//后台运行
    else
        state = FG;//前台运行
    if(argv[0] == NULL)  //命令行为空直接返回
        return;
    // 如果不是内置命令(用builtin_cmd识别和解释内置命令)
    if(!builtin_cmd(argv))
    {
        //在它派生子进程之前阻塞SIGCHLD信号，防止竞争 
        if(sigprocmask(SIG_BLOCK, &set, NULL) < 0)
            unix_error("sigprocmask error");
 
        if((pid = fork()) < 0)  //pid小于0说明fork创建子进程失败 
            unix_error("fork error");
        else if(pid == 0)  //fork创建子进程
        {
            // 子进程的控制流开始
            if(sigprocmask(SIG_UNBLOCK, &set, NULL) < 0)  //解除阻塞
                unix_error("sigprocmask error");
            if(setpgid(0, 0) < 0)  //设置子进程id 
                unix_error("setpgid error");
            if(execve(argv[0], argv, environ) < 0){
                printf("%s: Command not found\n", argv[0]);
                exit(0);
            }
        }
        // 将当前进程添加进job中，无论是前台进程还是后台进程
        addjob(jobs, pid, state, cmdline);

        // 恢复受阻塞的信号 SIGINT、SIGTSTP和SIGCHLD
        if(sigprocmask(SIG_UNBLOCK, &set, NULL) < 0)
            unix_error("sigprocmask error");
 
        // 判断子进程类型并做处理
        if(state == FG)
            waitfg(pid);  //前台作业等待
        else
            printf("[%d] (%d) %s", pid2jid(pid), pid, cmdline);  //将进程id映射到job id   
    }
    return;
}

/* 
 * parseline - Parse the command line and build the argv array.
 * 
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.  
 */
int parseline(const char *cmdline, char **argv) 
{
    static char array[MAXLINE]; /* holds local copy of command line */
    char *buf = array;          /* ptr that traverses command line */
    char *delim;                /* points to first space delimiter */
    int argc;                   /* number of args */
    int bg;                     /* background job? */

    strcpy(buf, cmdline);
    buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
    while (*buf && (*buf == ' ')) /* ignore leading spaces */
	buf++;

    /* Build the argv list */
    argc = 0;
    if (*buf == '\'') {
	buf++;
	delim = strchr(buf, '\'');
    }
    else {
	delim = strchr(buf, ' ');
    }

    while (delim) {
	argv[argc++] = buf;
	*delim = '\0';
	buf = delim + 1;
	while (*buf && (*buf == ' ')) /* ignore spaces */
	       buf++;

	if (*buf == '\'') {
	    buf++;
	    delim = strchr(buf, '\'');
	}
	else {
	    delim = strchr(buf, ' ');
	}
    }
    argv[argc] = NULL;
    
    if (argc == 0)  /* ignore blank line */
	return 1;

    /* should the job run in the background? */
    if ((bg = (*argv[argc-1] == '&')) != 0) {
	argv[--argc] = NULL;
    }
    return bg;
}

/* 
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.  
 */
int builtin_cmd(char **argv) 
{
    if(strcmp(argv[0],"quit")==0) //如果命令是quit，退出
        {
	exit(0);}
    if(strcmp(argv[0],"jobs")==0) //如果命令是jobs，列出正在运行和停止的后台作业
        {
            listjobs(jobs);
            return 1;
        }
    if(strcmp(argv[0],"bg")==0 || strcmp(argv[0],"fg")==0) //如果是bg或者fg命令，执行do_fgbg函数 
        {
            do_bgfg(argv);
            return 1;
        }
    return 0;     /* not a builtin command */
}

/* 
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv)  
{  
    int num;  // 定义一个整数用于存储解析后的作业ID或进程ID  
    struct job_t *job;  // 定义一个指向作业结构体的指针，用于指向找到的作业  
  
    // 如果没有提供作业ID或进程ID参数，则输出错误信息并返回  
    if(!argv[1]){    
        printf("%s command requires PID or %%jobid argument\n", argv[0]);  
        return;  
    }  
  
    // 判断参数的第一个字符，以确定是作业ID还是进程ID  
    if(argv[1][0] == '%'){  // 如果参数以'%'开头，则解析为作业ID  
        if((num = strtol(&argv[1][1], NULL, 10)) <= 0){  // 解析'%'后面的数字为整数  
            printf("%s: argument must be a PID or %%jobid\n",argv[0]);  // 如果解析失败或数字不合法，输出错误信息  
            return;  
        }  
        if((job = getjobjid(jobs, num)) == NULL){  // 根据作业ID查找作业  
            printf("%%%d: No such job\n", num);  // 如果没找到对应的作业，输出错误信息  
            return;  
        }  
    } else {  // 如果参数不是以'%'开头，则解析为进程ID  
        if((num = strtol(argv[1], NULL, 10)) <= 0){  // 解析参数为整数  
            printf("%s: argument must be a PID or %%jobid\n",argv[0]);  // 如果解析失败或数字不合法，输出错误信息  
            return;  
        }  
        if((job = getjobpid(jobs, num)) == NULL){  // 根据进程ID查找作业  
            printf("(%d): No such process\n", num);  // 如果没找到对应的进程，输出错误信息  
            return;  
        }  
    }  
  
    // 根据argv[0]的值判断是前台执行还是后台执行  
    if(!strcmp(argv[0], "bg")){  // 如果是"bg"，则执行后台操作  
        job->state = BG;  // 将作业状态设置为后台  
        if(kill(-job->pid, SIGCONT) < 0)  // 向作业所在的进程组发送SIGCONT信号，恢复进程执行  
            unix_error("kill error");  // 如果发送信号失败，输出错误信息  
        printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);  // 输出作业信息  
    } else if(!strcmp(argv[0], "fg")) {  // 如果是"fg"，则执行前台操作  
        job->state = FG;  // 将作业状态设置为前台  
        if(kill(-job->pid, SIGCONT) < 0)  // 向作业所在的进程组发送SIGCONT信号，恢复进程执行  
            unix_error("kill error");  // 如果发送信号失败，输出错误信息  
        // 当进程被设置为前台执行时，当前程序（即shell）应等待该进程结束  
        waitfg(job->pid);  // 调用waitfg函数等待前台进程结束  
    } else {  // 如果argv[0]既不是"bg"也不是"fg"，则输出内部错误并退出程序  
        puts("do_bgfg: Internal error");  
        exit(0);  
    }  
    return;  // 函数执行完毕，返回  
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)  
{  
    // 定义一个信号集mask，用于sigsuspend函数中的信号掩码  
    sigset_t mask, prev;  
     
    //保存当前信号屏蔽字，并临时屏蔽SIGCHLD，避免被频繁唤醒
    sigemptyset(&mask); //初始化信号集mask，使其不包含任何信号  
    sigaddset(&mask, SIGCHLD);
    sigprocmask(SIG_BLOCK, &mask, &prev);//用prev保存原掩码
      
    // 循环检查前台作业是否完成  
    // fgpid函数返回当前前台作业的PID，如果没有前台作业则返回0  
    while (fgpid(jobs) != 0) {  
        // 使用sigsuspend函数暂停当前进程的执行  
        sigsuspend(&prev);        //暂停时取消阻塞 
    }  
     sigprocmask(SIG_SETMASK, &prev, NULL);//恢复
      
    // 当前台作业结束（即fgpid返回0），函数返回  
    return;  
}

/*****************
 * Signal handlers
 *****************/

/* 
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.  
 */
void sigchld_handler(int sig)   
{  
    // 保存原来的errno值，用于恢复  
    int olderrno = errno;  
    // 进程状态变量  
    int status;  
    // 进程ID  
    pid_t pid;  
    // 信号集，用于阻塞所有信号  
    sigset_t mask_all, prev_all;  
    // 初始化prev_all信号集为空集  
    sigemptyset(&prev_all);  
    // 初始化mask_all信号集为包含所有信号的集合  
    sigfillset(&mask_all);  
      
    // 循环调用waitpid，尽可能回收已终止或停止的子进程  
    while((pid = waitpid(-1,&status,WNOHANG | WUNTRACED)) > 0)  
    {  
        // 阻塞所有信号，防止在处理子进程状态时被其他信号打断  
        sigprocmask(SIG_BLOCK,&mask_all,&prev_all);  
          
        // 根据子进程的PID获取作业信息  
        struct job_t* job = getjobpid(jobs,pid);  
          
        // 如果子进程因为接收到SIGINT信号而终止  
        if(WIFSIGNALED(status) && WTERMSIG(status) == SIGINT && job->state != UNDEF)  
        {  
            // 输出子进程终止信息  
            printf("Job [%d] (%d) terminated by signal 2\n",job->jid,job->pid);  
        }  
        // 如果子进程因为接收到SIGTSTP信号而停止  
        else if(WIFSTOPPED(status) && WSTOPSIG(status) == SIGTSTP && job->state != ST)  
        {  
            // 输出子进程停止信息  
            printf("Job [%d] (%d) stopped by signal 20\n",job->jid,job->pid);  
            // 更新作业状态为停止状态  
            job->state = ST;  
        }  
          
        // 如果作业状态不是停止状态，则删除作业信息  
        if(getjobpid(jobs,pid)->state != ST) deletejob(jobs,pid);  
          
        // 恢复原来的信号掩码  
        sigprocmask(SIG_SETMASK,&prev_all,NULL);  
    }  
      
    // 恢复原来的errno值  
    errno = olderrno;  
      
    // 函数返回  
    return;  
}

/* 
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.  
 */
void sigint_handler(int sig)   
{  
    // 获取前台作业的PID  
    int fg_pid = fgpid(jobs);  
    // 获取前台作业的JID  
    int fg_jid = pid2jid(fg_pid);  
      
    // 如果没有前台作业，则直接返回  
    if(!fg_pid)    return;  
      
    // 定义信号集，用于阻塞所有信号  
    sigset_t mask_all, prev_all;  
    // 初始化mask_all信号集为包含所有信号的集合  
    sigfillset(&mask_all);  
    // 初始化prev_all信号集为空集  
    sigemptyset(&prev_all);  
      
    // 阻塞所有信号  
    sigprocmask(SIG_BLOCK, &mask_all, &prev_all);  
      
    // 根据前台作业的PID获取作业信息  
    struct job_t* job = getjobpid(jobs, fg_pid);  
      
    // 将作业状态设置为未定义状态  
    job->state = UNDEF;  
      
    // 向前台作业发送SIGINT信号（终止信号）  
    kill(-fg_pid, SIGINT);  
      
    // 输出前台作业被终止的信息  
    printf("Job [%d] (%d) terminated by signal 2\n", fg_jid, fg_pid);  
      
    // 恢复原来的信号掩码  
    sigprocmask(SIG_SETMASK, &prev_all, NULL);  
      
    // 函数返回  
    return;  
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.  
 */
void sigtstp_handler(int sig)   
{  
    // 获取前台作业的PID和JID  
    int fg_pid = fgpid(jobs);  // 调用fgpid函数获取前台作业的PID  
    int fg_jid = pid2jid(fg_pid);  // 调用pid2jid函数将PID转换为JID  
  
    // 如果没有前台作业，则直接返回  
    if(!fg_pid)      
        return;  
      
    // 定义两个信号集变量，用于阻塞和恢复信号  
    sigset_t mask_all, prev_all;  
      
    // 初始化mask_all信号集，包含所有信号  
    sigfillset(&mask_all);  
    // 初始化prev_all信号集为空  
    sigemptyset(&prev_all);  
      
    // 阻塞所有信号  
    sigprocmask(SIG_BLOCK, &mask_all, &prev_all);  
      
    // 根据前台作业的PID获取作业信息  
    struct job_t* job = getjobpid(jobs, fg_pid);  
      
    // 将作业状态设置为停止状态（ST）  
    job->state = ST;  
      
    // 向前台作业发送SIGTSTP信号（停止信号），使前台作业停止执行  
    kill(-fg_pid, SIGTSTP);  
      
    // 输出前台作业被停止的信息  
    printf("Job [%d] (%d) stopped by signal 20\n", fg_jid, fg_pid);  
      
    // 恢复原来的信号掩码  
    sigprocmask(SIG_SETMASK, &prev_all, NULL);  
}

/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job) {
    job->pid = 0;
    job->jid = 0;
    job->state = UNDEF;
    job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
	clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs) 
{
    int i, max=0;

    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].jid > max)
	    max = jobs[i].jid;
    return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline) 
{
    int i;
    
    if (pid < 1)
	return 0;

    for (i = 0; i < MAXJOBS; i++) {
	if (jobs[i].pid == 0) {
	    jobs[i].pid = pid;
	    jobs[i].state = state;
	    jobs[i].jid = nextjid++;
	    if (nextjid > MAXJOBS)
		nextjid = 1;
	    strcpy(jobs[i].cmdline, cmdline);
  	    if(verbose){
	        printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
            }
            return 1;
	}
    }
    printf("Tried to create too many jobs\n");
    return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid) 
{
    int i;

    if (pid < 1)
	return 0;

    for (i = 0; i < MAXJOBS; i++) {
	if (jobs[i].pid == pid) {
	    clearjob(&jobs[i]);
	    nextjid = maxjid(jobs)+1;
	    return 1;
	}
    }
    return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].state == FG)
	    return jobs[i].pid;
    return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
    int i;

    if (pid < 1)
	return NULL;
    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].pid == pid)
	    return &jobs[i];
    return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid) 
{
    int i;

    if (jid < 1)
	return NULL;
    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].jid == jid)
	    return &jobs[i];
    return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid) 
{
    int i;

    if (pid < 1)
	return 0;
    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].pid == pid) {
            return jobs[i].jid;
        }
    return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs) 
{
    int i;
    
    for (i = 0; i < MAXJOBS; i++) {
	if (jobs[i].pid != 0) {
	    printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
	    switch (jobs[i].state) {
		case BG: 
		    printf("Running ");
		    break;
		case FG: 
		    printf("Foreground ");
		    break;
		case ST: 
		    printf("Stopped ");
		    break;
	    default:
		    printf("listjobs: Internal error: job[%d].state=%d ", 
			   i, jobs[i].state);
	    }
	    printf("%s", jobs[i].cmdline);
	}
    }
}
/******************************
 * end job list helper routines
 ******************************/


/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void) 
{
    printf("Usage: shell [-hvp]\n");
    printf("   -h   print this message\n");
    printf("   -v   print additional diagnostic information\n");
    printf("   -p   do not emit a command prompt\n");
    exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
    exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
    fprintf(stdout, "%s\n", msg);
    exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler) 
{
    struct sigaction action, old_action;

    action.sa_handler = handler;  
    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
    action.sa_flags = SA_RESTART; /* restart syscalls if possible */

    if (sigaction(signum, &action, &old_action) < 0)
	unix_error("Signal error");
    return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig) 
{
    printf("Terminating after receipt of SIGQUIT signal\n");
    exit(1);
}



